Loud-speaker



May 8, 1951 R. c. HUNTER LOUD-SPEAKER Filed April 19, 1947 Patented May 8, 1951 UNITED STATES PATENT OFFICE 255L949v J: LOUD-SPEAKER.

Robert 0. Hunter, Cleveland, Ohio Application April 19, 1947,-Serial':N0. 742,599 (01. 179-1155) 2 Claims. 1

Thisginvention relates to an improved assembly ot a dynamic loud speaker, either of the permanent magnet type or the electro-magnet type. v .As is well known to those who are familiar with this particular art, the field assembly of a dynamic loud speaker comprises primarily a shell, a magnet'an'd a-pole piece. The pole piece extends into an aperture in the front wall or yoke plate of the shell with suflicient clearance to provide an annular air gap for location of the voice. coil therein, the voice coil being adapted to have axial movement therein under infiuence of the magnetic flux delivered by the magnet atth gap in which-the voice coil is located.

This: assembly usually includes also a diaphragm in the form of a cone whichis intended to set upv sound waves and which has the voice coil attached to its central neck portion, the voice coil consisting of a number of turns of finewire and carrying the voice current in accordance withthe sound that is reproduced. The voice coil being located in the air gap in the yoke plate and hence in a magnetic field, the'pulsations of electric current in the voice coil will cause the same to vibrate in the surrounding magnetic field; and these vibrations will be transformed into sound waves by the. cone to which the voice coil is attached. 7

As will be understood, the permanent magnet or electro-magnet creates a radial flux in the annular air gap which is of short radial extent and in which the voice coil is held concentrically for movement therein in accordance with the voice current that is impressed thereupon. The radial magnetic field is everywhere at right angle "to .the coil and hence to the direction of flow of current therein. Therefore the motive force that is due tothe interaction of the two magnetic fields is always in a direction at right angles to both the radial field and the general plane of the voice coil of wire, this motive force being exerted in an axial direction.

Thus considerable significance attaches to the radial flux and the co-ordination of the same with the voice coil; and thus it is required that the parts be assembled and maintained in proper relative arrangement so as to ensure continuing functioning in the manner intended with the requisite efficiency over a long period of time.

The magnetic field or flux being radial, the

proper assembly and maintenance of the parts in of time; and this consideration forms the basis of my presentinvention.

There have been previous attempts to ensure maintenance of the parts in their proper positions over-a prolonged period of time but such devices-have not been able to withstand the usual treatment to-which subjected or they have proved comparatively expensive in the cost of parts and the-time required for the assembly of the same.

Therefore the general object of my present invention is to provide a device'which is not only capable of producing the desired results, as above pointed out, but which is of decidedly more practical construction than any heretofore known to me. i

More specifically, it is an object of mypresent invention to devise a loud speaker with means for ensuring permanency of a uniform air gap about the pole tip and hence permanency of the proper relative. positioning and proper "functioning of the voice coil therein so as to thereby ensure tone reproduction in an efficient and dependable manner over a long period of time and without disturbance by such misuse as would otherwise disrupt properperf'ormance.

Another object is to devise such an assembly that is capable of producing the improvement above noted and that can be manufactured with minimum number of parts and can be assembled in a convenient and comparatively inexpensive Another object is :to devise such an improved assembly in which either a permanent magnet or an electro-magnet may be employed, with the same resulting advantages as above briefly noted and aswill be hereinafter more fully set forth.

Other objects will appear from the following description and claims when considered together with the accompanying drawing.

Fig. l is a sectional view of one form of my presentrdevice;

Fig. 2 is axview taken on'line 2--.2 of Fig. 1; Fig. 3. is-a view taken on 'line33 of Fig. 1;and

Figure 4 is a sectional view of another form of my invention.

, Inothe present. embodiment of myainventionfl' central aperture of the centering member 2; and

the cone-shaped dust cup or pressure cup 4, which is made of non-magnetic material, is affixed at its rear annular edge about the shoulder portion of the pole tip 3 and has the forward annular edge portion thereof in centering wedging engagement about the correspondingly formed conical surface 5 provided upon the centering member 2. The conical surface 5 forms the inner wall of an annular groove 2a in the inner face of the centering member 2', although such groove is not necessary so long as the edge of the pressure cup 4 does not bottom upon the member 2. That is, these parts are so constructed and arranged that the pressure cup 4 is at all times capable of self-centering engagement with the conical surface 5 and without any hindrance to the required wedging engagement between these two conical surfaces.

By having the conical surface 5 truly concentric with respect to the central aperture in the member 2, such wedging engagement between the two conical surfaces, as above explained, will ensure true' concentric positioning of the pole tip 3 within the aperture provided therefor, in such manner that the pole tip 3 will be uniformly spaced from the edge of the central aperture of the member 2.

Positioned between the rear enlarged end of the pole tip 3 and the rear wall of the shell I, there is the magnet 6 which may be either a permanent magnet or an electro-magnet. In this first form of device, I have indicated a permanent form of magnet; while the other form of device will be described later herein.

Between the pole tip 3 and the edge of the central aperture of the centering member 2, there is provided suitable space to accommodate the voice coil 1 upon the neck of the diaphragm.

The member 2 serves also as a means for centering the basket 8 of the diaphragm 9, the basket 8 having an inner marginal annular fiat portion 8a welded or otherwise attached to memher 2 and having its inner edge in centering engagement with an annular shoulder ll) of the member 2.

The member 2 may be formed upon a screw machine or as a metal stamping and, as above stated, the shell I may be formed as a stamping. The magnet 6 and the pole tip 3 with its dust cup may be assembled within the shell 1, these parts to be recognized as a unit; and the basket 8 with its diaphragm 9 may be attached to the outer surface of the centering member 2', these parts to be recognized as another unit. Then these two units may be connected together by means of the screw-threaded engagement between the member 2 and the shell I.

These parts are so constructed and arranged that there will be permanently assured the proper clearance for the voice coil by virtue of the-fact that the pole tip 3 will always occupy proper position concentrically therewithin. This true anddependable concentric arrangement is established and maintained by the bottomless" interengagement between the wedging conical surfaces of the dust cup, which is fixedly connected to the pole tip 3, and the corresponding conical surface provided upon the centering member 2.

Such an assembly is of course apt to be subjected to considerable shock from rough handling in the method of quantity production or from subsequent accident or abuse; and the normal arrangement and operation of the parts will be disturbed if not entirely disrupted except for my present provision.

As a result of my present arrangement, the device is ensured against accidental dislodgement or disturbance of parts by undue shock, as would otherwise result; and consequently my present invention is capable of most efficient performance over a longer period of time than would otherwise be possible and is not apt to require the attention necessary in other instances of such devices or to fall in absolute disuse as the result of misuse or abuse to which these devices may ordinarily be subjected. At the same time, my present form of invention will permit servicing and re-servicing of such devices instead of discarding them; and thus there may be realized a decided saving, as compared with other constructions.

The centering member 2 may be most readily placed in position; and the manner of attachment of the basket 8 thereto serves also to facilitate the assembly of these two parts as a unit. The several parts of the entire assembly are so co-ordinated as to permit removal of the one unit from the other; while the pole tip and magnet may both be readily removed from the shell I. The several parts are adapted to be held together without any other securing means. As will be apparent, my entire device may be manufactured and assembled at a comparatively low cost as to labor and parts; and the item of loss from discarded assemblies because of fail ure to meet the requirements upon actual test, is reduced to practically nil.

The primary advantage resides in the selfcompensating and self-centering feature of the member 2 and the manner of engagement between the conical surface portion thereof and the correspondingly formed dust cup, as above explained. Not only have I provided a centering means but my particular structure ensures a truer and more dependable centering arrangement of the parts. Also, as above pointed out, this same member 2 serves as a centering means in two respects.

I will refer now to an electro-magnet type of loud speaker which embodies my present invention. In this second form, the shell 28 which may be a metal stamping, has the core pole piece 2| inserted within a central aperture thereof for co-operation with the electro-magnet 22 which is mounted within the shell 28. The auxiliary member 23 of non magnetic material, is snugly fitted around the core pole piece 2! and is provided with an annular conical surface 24 which is inclined forwardly and inwardly, this surface 24 being intended for co-operative engagement with a companion conical surface portion 25 upon the yoke plate 26. Here, as in the first form of device, all parts may be made of steel except the non-magnetic members 4 and 23 and the parts are held in assembly by the yoke plates 2 and 2B. The pole piece 2| may have drive fit in the shell 20. The plate 25 has screw-threaded engagement within the forward end portion of the cylindrical shell 20. The purpose of this manner of engagement between the co-operating conical surface portions 24 and 25 is to ensure true centering of the core pole piece 2| within the central aperture of the yoke plate 26 so as to thereby establish and maintain the proper gap between the pole piece 2| and the yoke plate 26 for the voice coil, as explained in connection with the first form of device above. Such interengagement between the conical surfaces 24 and 25 will ensure also effective engagement of the member 23 with the core pole piece 2|.

In this second form of device, as in the first form described above, the yoke plate has an annular shoulder 26a for centering engagement with the inner annular edge of the diaphragm basket 21 which is afiixed thereto.

This second form of device possesses the same advantages as above noted in connection with the first form of device.

What I claim is:

1. In a loud speaker, a magnetic field assembly comprising a shell having a front wall with a centrally located aperture therein, said front wall having a rearwardly and inwardly tapering surface portion provided upon the inside thereof, a pole tip provided with an outwardly and forwardly tapering cup having a straight edge in centering wedging engagement with the inner surface of said first-named tapering surface portion, and said pole tip extending concentrically within said aperture in such manner as to provide an annular air gap for location of a voice coil therein, and a magnet engaged between said pole tip and the rear wall of said shell.

2. In a loud speaker, a magnetic field assembly comprising a shell having an annular open front end, a centering yoke plate. having engagement within the open end of said shell, said yoke plate having an annular groove provided upon the inner side thereof, the inner wall of said groove being of conical form tapering rearwardly and inwardly, a pole tip provided with an outwardly and forwardly tapering cup having a straight edge in centering wedging engagement with only the inner surface of said first-named tapering portion, and said pole tip extending concentrical- 1y within said aperture in such manner as to provide an air gap for location of a voice coil therein, and a magnet engaged between said pole tip and the rear wall of said shell, the tapering portion of said pole tip being at all times free of engagement with the bottom of said groove so as to permit complete compensation in establishing and maintaining centering interengagement between the parts.

ROBERT C. HUNTER.

REFERENCES CITED The following references are of record in the 

